Test partitioning script in various scenarios

Scenarios:

ISO on DVD with UEFI
~~ISO on DVD with Legacy BIOS~~ (already exercised by automated test suite)
ISO on USB with UEFI (we don’t support this, but I still want to know what happens)
ISO on USB with Legacy BIOS (we don’t support this, but I still want to know what happens)
USB Image on USB with UEFI
~~USB Image on USB with Legacy BIOS~~ (already exercised by automated test suite)
USB Image after first boot on {UEFI, Legacy BIOS}

Original created by @segfault on 16057 (Redmine)

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